1. Field of the Invention
The present invention relates to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive, and, in particular, to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive for recording data at high density and reproducing the data thus recorded at high density.
2. Description of the Related Art
Recently, as optical recording media (optical disk, magneto-optical disk and so forth) come to have large capacities, low costs, high reliabilities, and so forth, they have become used in various fields such as recording/reproducing of image information, recording/reproducing of various code data in computer systems, and so forth.
Especially, optical disk drives are demanded to have further large capacities, and need to use recording/reproducing methods of recording data at high density, and reproducing with high accuracy the data recorded at high density.
As a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto optical recording media, a method of shortening of laser wavelength and relative shortening of spot diameter through improvement of numerical aperture (NA) have been performed, for example.
Further, as a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto an optical recording medium of a magneto-optical recording system, shortening of record mark through magnetic-field modulation recording has been performed, for example.
In the related art, for optical recording media in the magneto-optical recording system, record marks through magnetic-field modulation recording are recorded successively with portions thereof overlapped with one another, a recording density in a track direction (referred to as a line density, hereinafter) is increased in comparison to a track width, and, thus, the total recording density is increased. Further, the track width is shortened, a recording density in a radial direction (referred to as a track density, hereinafter) is increased, and, thus, the total recording density is also increased.
Thus, in order to increase a recording density, a line density is increased, and/or a track density is increased.
However, when a track density is increased, in a case where interference of diffracted light is used as in a tracking error detecting system employing a push-pull method, a tracking signal is degraded when the track width is shortened to be less than a predetermined width. For example, in a case where a laser wavelength is 650 nm and a numerical aperture is 0.6, the tracking signal is degraded when the track width is less than approximately 0.505 xcexcm. Accordingly, there is a limit of improvement in track density.
When a line density is increased, because record marks are record successively with portions thereof overlapped with one another, crescent patterns of the record marks come to be emphasized. Such crescent record marks have curvature at end portions thereof increased when the track width increases, and portions which are not effective for reproducing increase.
Especially, in a case of MSR (Magnetically-induced Super Resolution) medium of double mask type, the crescent pattern of a record mark and a reproducing aperture (magnetic window) are exactly reverse in curvature. Accordingly, a resulting reproduced signal is degraded.
Thus, there is a limit of increase in recording density for each of the methods of increasing line density and increasing track density.
The present invention has been devised in consideration of those points, and, an object of the present invention is to provide an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method and an optical disk drive by which it is possible to record a plurality of rows of data in a single track, and reproduce the thus-recorded plurality of rows of data.
An optical disk recording method of recording data on an optical disk by applying laser light to a track of the optical disk, according to the present invention comprises the steps of:
a) driving a plurality of laser light sources in sequence in a time division manner, and applying a light flux to one track of the optical disk successively; and
b) producing a plurality of rows of record marks in the one track.
In this method, a plurality of laser light sources are driven in sequence, and a light flux is applied to one track thereby in sequence. Then, a plurality of rows of record marks are produced in the track of the optical disk. At this time, because the plurality of laser light sources are driven in sequence, there is no case where a plurality of light fluxes are applied simultaneously. Accordingly, it is possible to produce a plurality of rows of record marks in one track, avoiding optical interference between the plurality of light fluxes.
In order to improve the recording density of the optical disk, it is preferable that the step b) produces the plurality of rows of record marks in such a manner that the rows of record marks overlap partially with one another.
In this method, because the rows of record marks overlap partially with one another, it is possible to improve the line density. Further, because the plurality of rows of record marks are cut off by one another at the end portions thereof, it is possible to prevent the curvature of the record marks from increasing. Accordingly, it is possible to reduce problems that the curvature of the record marks and the curvature of the reproduction aperture (window) do not coincide in MSR (Magnetically-induced Super Resolution) reproduction by which record marks smaller than the beam spot can be reproduced using a magnetic mask. With regard to MSR reproduction of double mask type, see Japanese Laid-Open Patent Application No. 7-244877.
In order to apply the method to a magneto-optical disk, a magnetic field may be generated in the track of the magneto-optical disk by one magnetic head.
In this method, it is possible to produce plurality of rows of record marks partially overlapping each other in one track of a magneto-optical disk through a simple configuration.
In order to reproduce data from an optical disk in which a plurality of rows of record marks are recorded in one track, with high accuracy, an optical disk reproducing method of reproducing data recorded on an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the present invention, comprises the steps of:
a) driving a plurality of laser light sources in sequence by a time division manner, and applying a light flux to one track of the optical disk successively;
b) causing reflected light to be generated from the plurality of rows of record marks by the incident light flux successively, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
c) demodulating the data recorded in the track from the reproduced signal according to a predetermined decoding algorithm.
In this method, a reading light flux is applied to one track, and reflected light is caused to be generated from a plurality of rows of record marks to which the light flux is applied, in sequence. The reflected light is signals changing according to states of the record marks to which the light flux is applied, and, from the signals, the data recorded in the track of the optical disk can be obtained through demodulation according to a predetermined decoding algorithm.
Interference occurs between respective reflected light from record marks of a plurality of rows of record marks to which a light flux is applied. Accordingly, the signal changing according to the states of the plurality of rows of record marks contains interference between the reflected light from the plurality of rows of record marks, and the data may be demodulated after sampling from the interference-containing signal, through a Viterbi decoding algorithm.
In this method, because the data is demodulated, after sampling from the signal containing interference between the reflected light from the plurality of rows of record marks, through a Viterbi decoding algorithm, it is possible to obtain more probable data through demodulation at high accuracy.
The process can be performed easily when reflected light from record marks generated according to a light flux applied thereto successively in a time division manner by a plurality of laser light sources can be treated as a single reflected light. Accordingly, the signal changing according to the states of the plurality of rows of record marks is obtained from converting the reflected light generated in sequence from the plurality of rows of record marks by the light flux from the laser light sources driven at a frequency equal to or higher than the Nyquist frequency into electric signals, and mixing the electric signals; and
the data may be demodulated through a Viterbi decoding algorithm after sampling at predetermined periods from the mixed signal.
In this method, because laser light sources are driven at a frequency equal to or higher than the Nyquist frequency, a plurality of light fluxes are applied to one track at very short intervals in sequence in a time division manner. Accordingly, a reproduced signal obtained from converting the reflected light and mixing it can be regarded as a reproduced signal obtained from applying one light flux to the plurality of rows of record marks simultaneously. Further, by demodulating the reproduced signal by the Viterbi decoding algorithm, it is possible to obtain more probable data at high accuracy through the demodulation.
Thus, it is possible to provide an optical disk recording method of producing a plurality of rows of record marks in one track of an optical recording medium in such a manner that the rows of record marks overlap with each other partially, and to provide an optical disk reproducing method of reproducing data from the thus-recorded record marks.
In order to achieve an optical recording medium having an improved recording medium, in an optical recording medium according to the present invention on which data is recorded as a result of laser light being incident in a recording track and a magnetic field being generated therein,
a plurality of rows of record marks are recorded in each track in such a manner that the plurality of rows of record marks partially overlap one another.
In the recording medium, because a plurality of rows of record marks are recorded in each track, it is possible to improve a recording density of record marks in a radial direction of the recording medium. Further, because the plurality of rows of record marks partially overlap one another, it is possible to further improve a recording density of record marks of the recording medium.
Further, because the plurality of record marks are cut off by each other at the end portions thereof, it is possible to prevent the curvature of the record marks from increasing. Accordingly, it is possible to reduce the portions of the record marks which are not effective for reproduction.
The optical recording medium may be a magneto-optical disk.
This recording medium can be achieved from a magneto-optical disk, for example, on which data can be rewriteable. The recording medium merely should be overwriteable, and may be achieved by a phase-change optical disk.
Thus, it is possible to provide an optical recording medium in which a plurality of rows of record marks are produced in one track of an optical recording medium in such a manner that the rows of record marks overlap with each other partially.
In order to achieve an optical disk drive which can record data in a track of an optical disk at high density, an optical disk drive for recording data on an optical disk by applying laser light to a track of the optical disk, according to the present invention, comprises a light-flux applying part driving a plurality of laser light sources in sequence in a time division manner, and applying a light flux to one track of the optical disk successively; and
producing a plurality of rows of record marks in the one track.
In this optical disk drive, a plurality of laser light sources are driven in sequence, and a light flux is applied to one track thereby in sequence. Then, a plurality of rows of record marks are produced in the track of the optical disk. At this time, because the plurality of laser light sources are driven in sequence, there is no case where a plurality of light fluxes are applied simultaneously. Accordingly, it is possible to produce a plurality of rows of record marks in one track, avoiding optical interference between the plurality of light fluxes.
In order to improve recording density of the optical disk, it is preferable that the light-flux applying part applies the light flux to the track in a manner such as to produces the plurality of rows of record marks in such a manner that the rows of record marks overlap partially with one another.
In this optical disk drive, because the rows of record marks overlap partially with one another, it is possible to improve the line density. Further, because the plurality of rows of record marks are cut off by one another at the ends thereof, it is possible to prevent the curvature of the record marks from increasing. Accordingly, it is possible to reduce the portions of the record marks which are not effective in reproduction.
In order to apply this optical disk drive to a magneto-optical disk, the optical disk drive may further comprise a magnetic-field generating part generating a magnetic field in the track of the magneto-optical disk by one magnetic head.
In this optical disk drive, it is possible to produce plurality of rows of record marks partially overlapping each other in one track of a magneto-optical disk through a simple configuration.
In order to reproduce data from an optical disk in which a plurality of rows of record marks are recorded in one track, with high accuracy, an optical disk drive for reproducing data recorded on an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the present invention, comprises:
a reading light-flux applying part driving a plurality of laser light sources in sequence by a time division manner, and applying a light flux to one track of the optical disk successively;
a reproducing part causing reflected light to be generated from the plurality of rows of record marks by the incident light flux successively, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
a demodulating part demodulating the data recorded in the track from the reproduced signal according to a predetermined decoding algorithm.
In this optical disk drive, a reading light flux is applied to one track, and reflected light is caused to be generated from a plurality of rows of record marks to which the light flux is applied, in sequence. The reflected light is signals changing according to states of the record marks to which the light flux is applied, and, from the signals, the data recorded in the track of the optical disk can be obtained through demodulation according to a predetermined decoding algorithm.
Interference occurs between respective reflected light from record marks of a plurality of rows of record marks to which a light flux is applied. Accordingly, the demodulating part may comprise:
a sampling part sampling at predetermined periods from the signal containing interference between the reflected light from the plurality of rows of record marks; and
a Viterbi decoding part demodulating the data from the thus-sampled data by a Viterbi decoding algorithm.
In this method, because the data is demodulated by sampling from the signal containing interference between the reflected light from the plurality of rows of record marks, through a Viterbi decoding algorithm, it is possible to obtain more probable data through demodulation at high accuracy.
Process can be performed easily when reflected light from record marks generated according to a light flux applied thereto successively in a time division manner by a plurality of laser light sources can be treated as one reflected light. Accordingly, the reproducing part may comprise a reproduced signal generating part converting the reflected light generated in sequence from the plurality of rows of record marks by the light flux from the laser light sources driven at a frequency equal to or higher than the Nyquist frequency into electric signals, and mixing the electric signals.
In this optical disk drive, because laser light sources are driven at a frequency equal to or higher than the Nyquist frequency, a plurality of light fluxes are applied to one track at very short intervals in sequence in a time division manner. Accordingly, a reproduced signal obtained from converting the reflected light and mixing it can be regarded as a reproduced signal obtained from applying one light flux to the plurality of rows of record marks simultaneously. Further, by demodulating the reproduced signal by the Viterbi decoding algorithm, it is possible to obtain more probable data at high accuracy through the demodulation.
Thus, it is possible to provide an optical disk drive for producing a plurality of rows of record marks in one track of an optical recording medium in such a manner that the rows of record marks overlap with each other partially, and for reproducing data from the thus-recorded record marks.
In order to form a plurality of rows of record marks in one track of an optical disk and record data at high accuracy, an optical disk recording method of recording data on an optical disk by applying laser light to a track of the optical disk, according to the present invention, comprises the steps of:
a) applying a light flux to the track successively in such a manner that the thus-incident light flux crosses the track to-and-fro obliquely; and
b) producing a plurality of rows of record marks in the track.
In this method, a light flux is applied to one track successively. Thereby, a plurality of rows of record marks are formed in the track. At this time, because the plurality of laser light sources are driven in sequence, there is no case where a plurality of light fluxes are applied simultaneously. Accordingly, it is possible to produce a plurality of rows of record marks in one track, avoiding optical interference between the plurality of light fluxes.
In order to reproduce data from an optical disk on which a plurality of rows of record marks are formed in one track, at high accuracy, an optical disk reproducing method of reproducing data recorded in a track of an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the present invention, comprises the steps of:
a) applying a reading light flux to the track successively for the plurality of rows of record marks in such a manner that the thus-incident light flux crosses the track to-and-fro obliquely; and
b) causing reflected light to be generated from the plurality of rows of record marks by the incident light flux successively, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
c) demodulating the data recorded in the track from the reproduced signal according to a predetermined decoding algorithm.
In this method, a reading light flux is applied to one track, and reflected light is caused to be generated from a plurality of rows of record marks to which the light flux is applied, in sequence. These reflected light is signals changing according to states of the record marks to which the light flux is applied, and, from the signals, the data recorded in the track of the optical disk can be obtained through demodulation according to a predetermined decoding algorithm.
In order to form one row of record marks in one track of an optical disk and to enable downward comparability, the light-flux applying part may cause the positions of the plurality of rows of record marks to be equal to each other.
By causing the positions of the plurality of rows of record marks to be equal to each other by making the positions in the track to be irradiated by the plurality of laser light sources driven in sequence in a time division manner be equal, it is possible to treat the record marks produced in the track as one row of record marks. Accordingly, the optical disk drive is downward compatible.
In order to reproduce data from an optical disk on which one row of record marks are formed in one track and to enable downward comparability,
the reading light-flux applying part may drive one of the plurality of laser light sources, and apply the reading light flux to the track successively; and
reproduce from a row of record marks recorded in the track by the incident light flux.
By reproducing from one row of record marks produced in one track by driving one laser light source of the plurality of laser light sources, it is possible to reproduce from the one row of record marks formed in the track. Accordingly, the optical disk derive is downward compatible.
An optical disk recording method of recording data on an optical disk by applying laser light to a track of the optical disk, according to another aspect of the present invention, comprises the steps of:
a) driving a laser light source and outputting the laser light;
b) controlling a position on which the thus-output laser light is incident in one track in a radial direction of the optical disk; and
c) producing a plurality of rows of record marks in the track, row by row.
In this method, a laser light source is driven and the laser light is output therefrom. At this time, a position at which the thus-output laser light is applied to is controlled in one track, in a radial direction of the optical disk. Because a plurality of rows of record marks are produced in the track, row by row, in sequence, it is possible to produce a plurality of rows of record marks in one track with one laser light source.
The present invention in the other aspect can also be applied to a magneto-optical disk.
Further, the plurality of rows of record marks may be produced such a manner that the positions of the plurality of rows of record marks are made to be equal to each other in a rotation direction of the optical disk, and the record marks the positions of which are equal to each other in the rotation direction are made to have the same state. Thereby, it is possible to achieve downward compatibility.
In order to reproduce data from an optical disk on which a plurality of rows of record marks are formed in one track, at high accuracy, an optical disk reproducing method of reproducing data recorded in a track of an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the present invention, comprises the steps of:
a) driving a single laser light source and applying a reading light flux to one track;
b) simultaneously causing reflected light to be generated from the plurality of rows of record marks by the applied light flux, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
c) demodulating the data recorded in the track from the thus-reproduced signal according to a predetermined decoding algorithm.
In this method, a reading light flux is applied to one track, and simultaneously causing reflected light to be generated from the plurality of rows of record marks by the applied light flux. The reflected light is signals changing according to states of the record marks included in a portion of the track to which the light flux is applied, and, it is possible to demodulate the data recorded in the track of the optical disk from these signals according to the predetermined decoding algorithm.
In order to achieve an optical disk drive recording data in a track of an optical disk at high density, an optical disk drive for recording data on an optical disk by applying laser light to a track of the optical disk, according to the other aspect of the present invention, comprises:
a laser outputting part driving a single laser light source and outputting the laser light; and
a light-flux controlling part controlling a position at which the thus-output laser light is applied to the optical disk in one track, in a radial direction of the optical disk, and
producing a plurality of rows of record marks in the track, row by row.
In this optical disk drive, a single laser light source is driven and the laser light is output therefrom. At this time, a position at which the thus-output laser light is applied to is controlled in one track, in a radial direction of the optical disk. Because a plurality of rows of record marks are produced in the track, row by row, in sequence, it is possible to produce a plurality of rows of record marks in one track with a single laser light source.
In order to reproduce data from an optical disk on which a plurality of rows of record marks are formed in one track, at high accuracy, an optical disk drive for reproducing data recorded in a track of an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the other aspect of the present invention, comprises:
a reading light-flux applying part driving a single laser light source and applying a reading light flux to one track;
a signal reproducing part simultaneously causing reflected light to be generated from the plurality of rows of record marks by the applied light flux, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
a demodulating part demodulating the data recorded in the track from the thus-reproduced signal according to a predetermined decoding algorithm.
In this optical disk drive, a reading light flux is applied to one track, and simultaneously causing reflected light to be generated from the plurality of rows of record marks by the applied light flux. The reflected light is signals changing according to states of the record marks included in a portion to which the light flux is applied, and, it is possible to demodulate the data recorded in the track of the optical disk from these signals according to the predetermined decoding algorithm.
Thus, according to the other aspect of the present invention, it is possible to provide an optical disk recording method of producing with one light source a plurality of rows of record marks in one track of an optical recording medium in such a manner that the rows of record marks overlap with each other partially, and to provide an optical disk reproducing method of reproducing with one light source data from the thus-recorded record marks.
Further, it is possible to provide an optical disk drive for producing with one light source a plurality of rows of record marks in one track of an optical recording medium, and for reproducing with one light source data from the thus-recorded record marks.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.